Bioproduction of rubratoxin in a glucose-mineral salts broth with nutritional supplements and metabolic inhibitors.

A sterile glucose-salts broth fortified with various metabolic inhibitors and nutritional supplements was inoculated with conidia of Penicillium rubrum P3290, and incubated quiescently at 28 degrees C for 14 days. Potassium sulfite and sodium metabisulfite at all test concentrations caused moderate reduction in rubratoxin formation; at high concentrations (greater than or equal to 2.7 X 10(-2)M) accumulation of fungal tissue was also retarded. Production of rubratoxin and cell mass was inhibited by p-aminobenzoic acid; syntheses of toxin were completely blocked by 7.5 X 10(-2)M of the vitamin. Effects of sodium fluoride on P. rubrum cultures grown on inorganic nitrogen sources varied from inhibition of mold growth and (or) rubratoxin A production to reduction in formation of rubratoxin B. With organic nitrogen sources, fluoride caused a 30 and 60% reduction in synthesis of rubratoxins A and B, respectively. Sodium acetate at all test concentrations enhanced formation of rubratoxin; mold growth was enhanced when acetate concentration was larger than or equal to 6.0 X 10(-2)M. A moderate reduction in mold growth was caused by lower acetate concentrations (1.2 X 10(-2)M or 2.4 X 10(-2)M). Sodium arsenite and iodoacetate at test concentrations blocked mold growth and toxin formation; sodium azide and 2,4-dinitrophenol caused a marked reduction in mold growth but inhibited toxin formation completely. However, sodium azide permitted slight growth and toxin formation when mold cultures were incubated for 28 days.